The Apollonicon was a large mechanical organ built around 1817 by
London Organbuilders Flight & Robinson for a hall in Bristol, but it
was cancelled and displayed at their factory in St. Martin's Lane.

The monumental instrument had five manuals and pedals and 45 stops
that can be played by a human performer, plus, it could be played
automatically by a pinned cylinder mechanism with three massive
cylinders two feet in diameter and eight feet long. The organ had
1900 pipes and two kettle drums played from the cylinders.

This is one of the earliest and largest player organs of the era.
The mechanical system was powered by a steam engine behind the organ.
Said engine may have also pumped the bellows when the organ was being
hand played.

Most interestingly, the stops could be changed by the cylinders with
an early form of a lock and cancel system. This system is described
in great detail in the Mechanics magazine 1828 issue. I will link a
copy at the end.

As mentioned above, the player system has three pinned cylinders
controlling what can be seen as a early form of Melody, Counter Melody
and Bass sections that make up modern mechanical organs. According to
the Encyclopedia, the registers available on the cylinders are

(1) on the first cylinder: open diapason, stopped diapason, principal,
twelfth, fifteenth, flute, sesquialtra and trumpet. This cylinder has
five complete octaves of notes.

(2) The second cylinder has only two octaves and plays a rank of large
wooden pipes, the lowest being GGG, this stop is technically 32' pitch.
There is also a rank of large reed trombones. These ranks can also be
played by the manual pedal board.

(3) The third cylinder has the most stops listed, being: ceroma, flute,
vox humana, octave flute, Hautbois, piccolo, trumpet, diapason, and
principal.

More stops likely exist, as there is "etc." listed at the end of the
list provided. The two kettle drums probably play from the cylinder
with bass pipes. It is stated that these have three beaters and
reiterate using a similar system to the clockwork snare drums on Imhof
barrel orchestrions, but driven by the main flywheel and not their own
springs.

The dimensions of the case are generally agreed to be 24' high,
20' wide and 18' deep. The console for hand-playing is detached so
that the player is facing the audience. The five keyboards, one
being five octaves and the others all three, all arranged in a row,
as opposed to "stacked" on top of each other on normal organs. This
supposedly allowed up to five people to play full orchestra parts on
the organ at the same time.

The facade is generally agreed to be decorated by four pilasters,
between them are three paintings of Apollo in the center, flanked
by Clio and Erato. These were painted by John Masey Wright. One
Dr. Hinton said that there was three sets of pipes visible below the
paintings. There is a drawing of an un-built hall in Bristol that
shows a detailed line sketch of the organ case; the first description
appears to be correct. The best I can do is provide a link to this:

https://www.architecture.com/image-library/ribapix/image-information/poster/unexecuted-design-for-the-interior-of-the-commercial-coffee-rooms-bristol-section-towards-the-apollo/posterid/RIBA35624.html 

There is a published engraving of the organ, but the paintings appear
to be covered by some sort of curtain or tarp. The very wide console
can be seen with multiple music racks for many musicians playing at
the same time. Behind this, it appears one of the cylinders is visible,
possibly behind glass. This engraving can be seen as Figure 1.

The organ has a long known history, built between 1812-17, and was most
likely planed for the Bristol hall, but the hall was not made or the
organ was not delivered. As such it stayed in the factory hall, where
it was reported on by Mechanics magazine in 1828. At some point the
builder Hill got his hands on the organ and he moved it to the London
Adelaide Gallery. Another rough line sketch shows it in this new
location in 1851.

It is noted that a rank of horizontal pipes appears to be
protruding from the roof of the case, a sign of alteration by Hill
(Figure 2). The organ was offered for sale by "the musical times"
in 1881, supposedly in good condition. After this, I have not heard
of the organ again. If it is still around, it is most definitely
heavily altered, and the cylinder system is probably gone. If you
have more info please contact me at the email below.

Christian Tedesco
cmt0817@gmail.com.geentroep [delete ".geentroep" to reply]

References:
Mechanics magazine:
https://books.google.com/books?id=GA0pAAAAYAAJ&dq=Mechanics%20Magazine%201828&pg=PA97#v=onepage&q&f=false 
Source of line drawing: https://web.archive.org/web/20120319212644/http://www.npor.org.uk/Reporter/apr02/g402.htm 

 [   Figure 1.
 [ https://www.mmdigest.com/Attachments/21/01/16/210116_220945_apollonicon%201.jpg 
 [   Figure 2.
 [ https://www.mmdigest.com/Attachments/21/01/16/210116_220945_apollonicon%202.jpg